We are continuing our studies of gene expression in rat liver cells with an emphasis on alpha-fetoprotein and albumin gene activity. In part, the rationale for these studies resides in the availability of sensitive assays for monitoring the expression of AFP and ALB genes during times such as fetal and neonatal development, liver regeneration, tumor growth, and carcinogenesis when fundamental alterations in mechanisms of gene expression might reasonably be expected to occur. Analysis and interpretation of quantitative as well as qualitative changes in the level of gene expression and a description of the methods used to regulate this expression are goals of our studies. Toward these ends we have developed assays for the transcriptional and translational activity of AFP and ALB genes and applied them to the study of gene expression in several biological systems of interest. We are presently focusing our studies on: (1)\defining the involvement of methylation of AFP and ALB structural genes or regulatory elements on transcriptional activity by examining restriction endonuclease digests of genomic DNA; (2)\refining methods to identify AFP mRNA-synthesizing putative preneoplastic cell populations in hepatocarcinogen-treated rats using in situ hybridization techniques; and (3)\using DNA transfection techniques to determine if there is a transforming gene in rat hepatomas and at what time and in what cell type(s) it appears during hepatocarcinogenesis. In these studies, we have found that there is little or no correlation between the extent of methylation and the transcriptional activity of either the ALB or AFP genes. This includes gene activation (or inactivation) during normal development and reexpression of the AFP gene during carcinogenesis in transplantable hepatomas, and in liver regeneration. Our efforts to find a transforming gene in the genomes of rat hepatomas were unsuccessful. DNA from the hepatomas 5123C, 7777, 9098, 9168A, and 1001 did not induce foci upon transfer into NIH 3T3 cells. Also negative in this assay were DNAs from oval cells, hyperplastic nodules, and primary liver carcinomas. We are now trying to find whether there might be alterations in the level of expression of some known oncogene during carcinogenesis and to screen for other possible tumor specific mRNAs. (M)